This invention relates to timing synchronization and, more particularly, to timing synchronization in wireless communications systems.
Recently, orthogonal frequency division multiplexing (OFDM) has been applied to communications systems and, in particular, to wireless communications systems. In OFDM a plurality of frequency multiplexed relatively narrow band signals are employed to form a wide band, xe2x80x9chighxe2x80x9d speed radio transmission link. In such an arrangement timing synchronization is required to position the signal in an optimum sampling window and to ensure proper alignment of the phases of the plurality of narrow band signals. To this end, it is required to obtain a timing adjustment signal that is employed to adjust timing in order to obtain the properly alignment.
Indeed, in multiple access systems based on OFDM, it is critical that there be synchronous arrival of mobile user symbols at a base station. If a particular user""s arriving symbols are offset in time relative to other synchronized user""s arriving symbols, the result is interference to the arriving symbols of all the mobile users.
In prior arrangements, attempts have been made to generate a timing adjustment signal through the estimation of all of the signal transmission channel parameters.
One prior known arrangement for estimating signal parameters is described in U.S. Pat. No. 4,750,147 issued on Jun. 7, 1988 which is commonly referred to as xe2x80x9cESPRITxe2x80x9d (Estimation of Signal Parameters using Rotational Invariance Techniques). The ESPRIT technique is based on maximum likelihood entropy principles, or subspaces, for the estimation of sinusoid signal parameters. As such, ESPRIT cannot be directly applied to estimation of signal parameters in an OFDM system because ESPRIT is directed toward extracting all of the signal transmission channel parameters and there is insufficient data to realize this. Moreover, extracting all the signal transmission channel parameters generally requires a large amount of measurement data, which either is not available or results in significant system overhead. Indeed, in an OFDM system there are just too many parameters for all of them to be uniquely identified as is required in the prior ESPRIT arrangement.
Problems and limitations of prior known arrangements and techniques for signal transmission channel parameter estimation are overcome by employing a unique arrangement and/or method that does not require the estimation of all the signal transmission channel parameters.
Specifically, this is realized by employing a rotational invariance arrangement or technique that utilizes either spectral, and/or temporal, and/or spatial diversity present in the wireless system to generate a single prescribed parameter of the mobile signal transmission channel.
The single prescribed signal transmission channel parameter is obtained by forcing the rotational invariance arrangement or technique to yield the single largest eigenvector from a prescribed relationship of signal data vectors of the signal transmission channel.
In one embodiment of the invention the prescribed parameter of the signal transmission channel is the delay that is substantially constant over the diversity, while the gain of each signal transmission channel path may vary. The estimated signal transmission channel delay is advantageously employed in a mobile station to adjust the timing alignment of the mobile signal being transmitted over the channel to the base station, thereby ensuring proper positioning of the transmitted mobile signal in the optimum sampling window at the base station.